Noble gas metallurgy



sept. 2s, 194s.

Filed April 5, 1945 G. R.O BURKHARDT NOBLE GAS METALLURGY 2 Sheds-Sheet 1 1N VIN'IOR GEORGE R.' BURKHAR DT Sept.y 28, 1948.l G, R, BURKHARDT V 2,450,081

NOBLE GAS METALLURGY Filed April 5, 1945 2 sheets-sheet 2 INvENIon GEORGE R. BURKHARDT Patented Slept. 28, 94

siren STA-TES PATENT OFFICE g,45o,os.1 NOBLE, ons METALLURGY este a soweit Chiaro, 111- appiieauqn anni 1945,'.seria1 No. ssasoe relaas.. 01- lfwfl-o v l f This application is a continuation in part ofimy pending application, Serial No. 523,'7D5, filed .Feb-` ruary 2li, 1944, Patent No. Zflli, for ffNoble gas metallurgy.

The present invention relates to a method for the treatment of a ferrous metal miren-carbon alloy and more particularly to an improvement in the metallurgy of steel by which a more corn'- pact and more minute crystalline structure is btained. By means ci the improved method as hereinafter described, dissolved embrittling gases, slag inclusions and other stress raisers 'are .re-

-nioved from the metal to an extent which .is Snot possible by other methods heretofore used.

` The-usual practice in the manufacture fof iron.- carbon alloys, or steel, Aresults `in a metal struc..- ture in which small amounts of slag are included, and in which dissolved gases, such as hydrogen, oxygen and other chemically active gases, are

present which substantially Hreduce .the strength of the metal.

In the manufacture of steel by the lBessemer process and the onen-hearth process, it is ldimcult to control the grain size .of .the productlfor the reason that the grain size isdependenttoa 1 considerable extent on the amount .of slag inclusions and other impurities present. .When metal produced by either of these nprocesses ispoured into molds or ingots, the metal contracts during cooling and solidication, by which cavities',1

known as pipes are formed, which frequently extend into the ingot such a distance that they are not removed when the top of the ingotor casting is cut off preparatory to the rollingopera- In these processes, spiegeleisen or ier-roman,- ganese is added for the purpose of supplyingthe proper percentages of manganese and carbon in the steel so as to obtain the desired rolling sproperties. It is known, however, `that While the manganese of the spiegeleisen or ferromanganese combines with dissolved oxygen in the metal and serves to decrease the blow-holes in :thesolid ingot, such blow-holes are invariably present and substantially weaken the metal. The presence or small proportions of slag also decreases VAthe strength of the metal by preventing ther complete union of metal particles in the steel. IIt is Vknown also that the presence of small proportions of slag in the metal affects the crystallization .or grain size of crystals in the metal.

Attempts have been made to remove ,oxidizing gases in ferrous metals as l'by introducing alblast of a noble gas into the converter `to dSplaceair .-:Erom themetal prior to the introduction Qffllydrogen, which is employedfor the purpose o i reducing the oxides present in the metal. Such use of a noble gas as a scavenger kto remove oxygen prior to the introduction of hydrogen has no substantial effect, however, on the physical or chemical properties ,of the metal. Attempts have also been made to employ nitrogen, helium, and other rare gases, by bubbling the gas through the molten metal to produce agitation, but no substantial improvement `in the physical properties of the metal has-been obtained by this bubbling method, and neither of these `prior methods has met with commercial acceptance.

It has been `found .that steel rails rolled from blooms or ingots which have been re-heated by the vusual lprior art 'methods frequently develop iissures -because the metal `has been made minutely porous .by elused gases.

The .presentinvention inthe treatment o f ierrous metal ,or iron-carbon alloys involves theuse .of a blanket or atmosphere of anoble gas which is ,preferably .employed at a `high pressure and which surrounds the ingo-t or metal Vunder treatment for a substantial period of time during which the metal is allowed to remain quiescent, .so as to 4permit voocluded or dissolved gases i e l'I netalto vbe ,dispersed into the noble gas, by they may be substantially completely removed from the metal. The dissolved gases generally include oxygen, nitrogen .and carbon monoxide,

whichbecome dispersed 0r diffused milie-body of the noble gas. The use of a noblegas )as ya 'blanket or 4atmosphere around the metal, Kpermits the :use of substantially elevated temper.- aturesto .be maintained without ,oxidizingelect on vthe metal ,and allows the dissolved and occluded gases thereinto be gradually ITemOfJQd, from the l substantial elimination .of `blow-holesin the r metal `without deleterious Aaction on .the metal underv treatment. As hereinafter explained, the noble as lf 1eli'urr1 be independently heated andthe maintenance of ...the lternp eratu r e ,during treatment `and then submetal in the noble gas at;-

.squentlccelineofthe' independently regulated,

,mosphere may be whereby the gr'ainlslzeof the crystalsin thelnal ,metal product maybe more completely controlled.

It will beun'derstood @thatfthe method yotthe present invention relates particularly to the treat,- A inent of .tlj 1 e hot solid metal containing austenite,

in the iorfrn of a .casting or ingot, andmay be .employ-ed directly in trie-treatment iof ,incitan .metal Afrom a Bessemer `converter or .openhearth ina ladle eri-prior t0-the Casting 0f 'bh inset 9.1

vv,it .may be -aiipledadiretly i9 :Cast ingo@ ,Weigh other noble gas, or member of the helium family,.

as argon, neon, Zenon or krypton, may be used, or a mixture of two or more of these gases may be employed. The noble gas may be independently heated during the treatment of the metal, or prior thereto, or the metal under treatment may be separately heated to provide a temperature of the steel or iron-carbon alloy at which austenite is present, so as to maintain the metal at a desired temperature during a period of quiescence in which dissolved or occluded gases in the metal may be dispersed into or taken up by the noble gas. It has b een found preferable to subject the ferrous metal during a period of quiescence to an atmosphere of the noble gas both before and after it is rolled, and permitting the metal to cool in an atmosphere of the noble gas, as the metal adsorbs injurious gases if subjected to atmospheric air during slow cooling.

The importance of reheating or soaking an lngot or casting ina noble gas is apparent from a comparison of the physical properties and microstructure of steels treated by this method with those of steels treated by the ordinary methods heretofore used. The improvement in the properties is believed to beassociated with a change in space lattice or porosity of the metal which takes place when the metal is heated to the temperature at which austenite is formed. This change in space lattice or porosity of the metal generally takes place between 1330 and 2550 F., between which temperatures austenite occurs in simple steels having less than about 1.7% of carbon. It Will be understood, of course, that austenite is a solid solution of carbon in gamma iron, and occurs between the solidus and the liquidus of the equilibrium diagram for ironcarbon alloys. i

In the method of the invention, helium gas is preferably employed under a pressure of from about 1000 to 4000 pounds pressure per square inch, the temperature of the gas being controlled by the addition of heat, if necessaryso as to maintain the metal during the period of quiescence in the condition in which austenite is present, during which the pores of the metal are open and the occluded and dissolved gases in the metal may be readily removed therefrom by being dispersed or dissipated into the body of the helium or other noble gas employed.

The heat conductivity of helium is greater than that of any other gas with the exception of hydrogen, which follows from the kinetic theory of gases, since except for hydrogen it has the smallest molecular weight of any `gas and therefore the highest molecular velocities at a given temperature. Helium transfers its kinetic energy, therefore, from molecule to molecule more rapidly than any other gas, with the exception of hydrogen. rlhe thermal conductivity of helium is .000339 at C., as compared with .0000568for air at 0 C. The thermal conductivity of helium is therefore about six times that of air, so that heat may be added to or abstracted from a metal by means of helium about six times as rapidly as with air, and the helium has the advantage, furthermore, that the metal is unaffected thereby at any temperature, Whereas in the presence of air, the metal is oxidized to a substantial extent at high temperatures.

The heat conductivity of a gas is independent of pressure through a wide range, and in cooling the metal in contact with helium, or other noble gas, in accordance with this invention, the gas operates as a protecting layer and prevents ac- `cess of chemically active gases, such as air, until the metal is cold, or cooled to the extent that it is unalected by the air at room temperature. It will be understood that helium and other gases of the helium family are monatomic, that is, the molecules of these gases are atoms and do not dissociate to form atoms in the nascent state so as to react chemically with other materials. Hydrogen, on the other hand, is diatomic, that is, the molecule of hydrogen, Hz, is composed of two atoms of hydrogen, H, having a single bond or Valence, so that when the gas dissociates to form the hydrogen atoms, it readily reacts chemically with other substances present. The noble gases, unlike most other gases, are inert and are not dissolved or occluded in metals and do not enter into chemical combination with the metals or other materials present under the conditions of operation in the treatment of metals in accordance with the invention hereinafter more fully described.

In carrying out the method of the invention, the noble gas, as helium, may be purified and recycled during the operation or treatment, or puriiied periodically from time to time as required, depending upon the particular metal composition treated, or the amount of dissolved and absorbed gases in the metal treated. The method of purification to be employed depends, to some extent, on the particular conditions of operation, but ordinarily the gas may be puriiied by first passing it through soda-lime, in order to remove carbon dioxide, then through calcium chloride to remove water vapor, then through heated copper to remove oxygen, and also to remove hydrogen, if present, by combination with oxygen to form water vapor, then through calcium chloride to remove water vapor, if present, and finally over heated magnesium or calcium to remove nitrogen.

It will be understood that a gas, exclusive of the noble gases, when in contact with a metal is held in contact with the surface thereof through molecular forces which produce more or less condensation of the gas on the surface of the metal. The gas also permeates the pores of the metal and is condensed on the surfaces of the pores, which phenomenon is referred to as occlusion When steel is subjected to an atmosphere of a noble gas, as helium, at a temperature at which austenite is present in the steel, the gases held on the surface of the metal and in the pores by condensation and occlusion are gradually diffused into the body or blanket of the noble gas, following the law of diffusion of gases into each other, so that the condensed and occluded gases are progressively removed by the noble gas. If the noble gas is heated to a higher temperature than that of the metal under treatment, the heat from the gas is rapidly transferred to the ingot or metal because of the high conductivity of the gas, as helium, irrespective of the pressures which are used, and by the removal of the injurious gases, the metal product which is produced is aandoet A more homogenous fthanrsthe metalf .product produced by other prior' a'rt sinoe'blow-holesare 'substantially elim.- inated anditheproduct is notV subject to atmoscorrosi'on asis the. case with steel or ironc'anbort alloys-producedby methods oirthe prior sari; Y

One-.ofthe objects of the invention is toprovide a-method for the treatmentl of iron-carbon alloys in thesolid state in which a substantially larger proportion of dissolved or occluded gases may be removed.` from the metal than by any of the methodszfheretotoref used. n accordancewith this; ciale-ct of. the invention, the method hereinafter-described provides forl the treatment of the metal' in theisolid state at a temperature at' which anstenite. is,vr present with a` noble gas, as helium, ma mannen so-that the metal may lie undisttnvbedor quiescent inthe gas for a periodoftime sumoientftofpermit occludedand dissolvedL gases in-Jtha metal tot be dispensed or dissipated intothe body ofr the surrounding. noble gas.

Anotherobfject isftof provide a Vmethod for the treatment-oi'steeli or iron-carbonV allo-ys, which pernnts the castingtot ingots: or castings by the usuateoxrunercial'processes,y after which the'i-ngots or castings may be subcctedn a heated condition to' anfatmosphereoihelium or other noble gas at a; temperature at which austenite is present in the metalgg. the ingfot: rorcasting being treated or allowed 1to1-remain quiescent in the noble gas for aperiod of time suihcient to permit dissolved on occluded. gases in the metal to be taken up by the-body ofithe noble.- gas, thereby removing blowholes-tifomY themetal and substantially increasing the. tensile: strengths and other desired properties of the-metal. y

`Aufurtller obect istoprov-idea method for the treatment ot steel castings or ingots at a temperatnize atfwhichl austenite is present in thefmetal, orf/.subjecting it .tof an atmosphere of a noble gas in whichz themetal remain in contact with saidgas for a period of time suiicient to; permit occluded and dissolved gases to be eiiused from thefmetal and dispersed intothe noble gas-,which thereafter. be chemically purified to remove car-,bon dioxide, Water vapor, oxygen, hydrogen, nim-ogenr and other undesired constituents;

Another objectsisto providea method for the treatment of. iron-carbonv alloys or steel` in; the solid-v sta-te;` im the" form ofv casting-s, ingots' or bloomst to removef oceluded, condensedI and dis-- solved foreign gases; and7 to eliminate-bloW-holes and other imperfections-in the meta-l While it remains. quiescent in the austenic condition-inf a mannensuch that,themetal,iscoinpressedv or corn-Y p'vactediy under a.high pressure, so that-the'metal isfrendered less subject to corrosion by contact with theaiatmosphere afterit has been cooled. Another object isl to prov-idev a continuous method for the.treatmenty of'ingots or steelcasting-s, in Whichf the ingots or castings may/be successivelyitreated: in hotter and hotter helium, or nobletgastby the'.abstractionV of heat from the mgots-orcastinea as itis passed progressively through the system; and inY Which the noble gasv may befusedfas a cooling medium for the outgoingv ingo,ts, by.which theiingots maybe cooled to room.y temperature at, the` out-going. end of` thee system, andwhereby heat.is:abstracted from the ingots, or castingsfby'the. application. of the. counter current principle. infthef system, so that. as the treatment' ofonef ingQtorca-Sting is. conuoletedJ and is re,- moved ironi-V the,- systernat vthe out-going, endg. another inset, Ineas be inserted into-the 'system- 6 at theincomtngterfd thai-line, thereby renden inathermethod-suhstantialiy contmiimas.

A stili;'furtherr obj ect isf tov providefafcontmuous method for the treatment otsteelingotsiandl castings -in'f a; sufcientlyfheated conditiomto lcontain austen-ite; vby 1subcting the-meets or. castings; as the-y advance. inthe system; to successively .purer and purer? heliurnf,L or other noblegas; infy a manner to; progressivelwremoveoccluded; condensed! and dissolved ioreigni gases; from. the* metal,l and: con trolling; the coolingV of; thefmeta'l then'obie' sofas not.` to expose the metals-to"the-atmosphere until'. it is ata temperature'rat whicnfthemetal is unaitected thereby,A wherebyfthe metal issub stanti-ally compacted-so as'I yto remove bloweholjes inthe metaL-and a.V uni-torna,4` mie-grained metal productfis obtained.A

The: irnzentiomisexplained in detail: in connestionwith va'riousffurnis of: apparatus which. may bef; employed in carrying out the inventionr4 afsillustrated.- inY the accompanying.v drawing-s1; in which: v

Figurev l-:Iis an eicvational. view-.- partlydnf-section., of an irrgot,A mold' illustrating .ant application of, the invention, in which. a'storagetank forth-e nobleA gas-jandconneotions to the m'oldtogether with apparatus for purify-ingl the eas,v4 arediagrammaticall-y indicated Figurer 2: is a.- pian View' of;` apparatus villustratingtheI use of: theiinverntioninconnection.Lv ineots` on the conventional. fingot car; andi" Figure Bris, a View i-n elevation, partly i-nrsectiorr,A illustratingthe. application ofthe invention toan ingotmold oi lthe bottom poured type.

Refer-.fina tof the f severar` dravi/inns: illustrating variousgapplicationsfof the: imentiongl tliepr cedute in carrying fout* the noivelY frniethodiinffcoriaf nection Withthe apparatusshownfinFig.l 1v ofthedraw-ings is as follows:

Asi-here; shown the-'-ir-tgotfmoldiL is designa-tediouthereferenceietter I.- andv toj carryoutfthlespresent' inuentionthera is: associated. with thi'simoldfagasfeeding; head IKS desi-gned'to beproperiyfitted over and! into.' the upper endof the:rnoldfandA provided.

withfarnoblergas.- intake: I1, a suitablefoperated intake valve l,8.-,. a combined.' feeding and exhaust noch-*Io snugly ttingfwithin the'f upper openend ot. the ingot mold, an exhaustoutlet 2'0 opposite theA gas intaket'lfamdr` a suitably designed andi suitably# controlled. valve 'Z l' for opening and clos--I ina the gas;exhaustZi);v In explanation ofthe invention as carried( outiin connectionavitlranf ingotmoldcand a gas feeding-.head i 6;, as iasiiowny ini/Fia.; l ot the draw-ings,` it iste be noted that the noble -gas-r is contained. in suitablefsupply tanlrsfor; tank; cars.- 23f-,--.unden a, Ahigh pressure-,ssl from: G-to- 4009; poundsfperf squareA inch,A and 'ther maintained pressure-therein is: suiilci'enty torpump: out the atmosphere inv the 'mold-,f or it: desired; supplemental' pumping; means4 3-mayr be usedr. In practice the. molten-metal is poured into* the? ingot-mold) I andthe-1 gasy feeding-:- head2 l 6 isifhenr inserted intofthe.opentopofthemold';- The valves trand 2:15y arethenl' openedtandthefair in) the-mold. is displaced; bythe incoming'v noble` gas, from the.'Y pipeA 32e. after. which. thefvaiuer 2d ot the exhaust: outlet-20 is closed and the pressure o-lfthev noble1 gas: srbuiltf ups until `the.metal, co oled; to: ai pasty consistency',isrthoroughiy compressedby'pressura onv the topfand.- sides-.of the in'got;v Then,` arten-afi predetermined-married off, soaking the: ingot. irr the heated noble gas-,fsuchz as aeperiodbt from: one to lnue,F hoursr. thefexhaust fvaivee v2 I--'V isf opened!y tofpermitthenoble gastobefcollected fon neusez.

'Imefgasiswingfrromrthe outlet-immun baronne# 7 ducted through a pipe 34, having a pump 36 therein, and from thence to a purifying apparatus containing chemicals for the removal of impurities from the gas, such as carbon dioxide, water vapor, oxygen, nitrogen, or other gaseous impurities, as hydrogen, which may have been taken up by the helium or other noble gas used while it is in contact with the heated ingot or casting. The carbon dioxide may be removed by the use of soda-lime, for example, in a container 38; water-vapor may be removed from the noble gas by means of calcium chloride in a container 4D; oxygen may be removed by means of heated copper in a container 42, in which hydrogen, if present in the gas, will react with the oxygen to form water-vapor, which may then be removed by the use of calcium chloride in an additional container, not shown, and finally, nitrogen present in the gas may be removed by means of magnesium or calcium in a container 44, in a manner Well known by those skilled in the art. From the container 44, the gas may be conducted through a pipe 46 to a storage tank 48, from which the gas may be subsequently drawn for treatment of the next ingot in a series, or for treatment of a series of ingots or castings in a system, as hereinafter more fully explained. It is to be understood that the purification steps above described may be varied as may be found desirable, or additional purification steps and other chemicals may be added, and the puriiicaytion steps above indicated are merely for purposes of illustration. It may be found desirable, to remove oxygen while the gas is in a highly heated condition, and then to remove nitrogen while the gas is still at a high temperature, after which the gas may be cooled somewhat to remove carbon dioxide and water-vapor.

In the illustration of Figure 2, it is to be noted that the ingots on the ingot car 22 are followed by a gas tank 23 mounted on a car 50. It will be understood that during transportation Vof the ingots in the ingot car 22, helium or other noble gas may be passed through pipe l1 from the tank 23 on the car 50 to the gas feeding head I6, through the intake valve I8, through the feeding and exhaust neck I9 from thence through a bleed valve 52, which may be provided in a casing of the ingot mold I, positioned above the level of the top of the ingot therein, through which air may be expelled during the admission of the helium or noble gas to the mold until helium gas passes out of the opening 52. The point at which the bleed valve at 52 should be closed may be readily determined by spectometry or by the simple expedient of a lighted match or its equivalent held at the opening 52, since helium or other noble gas will not support combustion. As soon as the lighted match is extinguished, indicating a high proportion oi helium issuing from the outlet, the valve at 52 `should be closed in order to prevent substantial loss of the noble gas. In the use of a series Iofingots on the ingot cars in carrying out the method of the invention, the iirst mold I6 is rst lled with helium, or the noble gas used, and the valve 2l may thenbe opened whereby the gas then passes through the exit pipe 20 to the ingot mold I6' next in the series, by opening the admission valve I8 and admitting the gas to the ingot chamber. After the ingot mold is filled with the noble gas, the bleed valve, similar to that used at 52, is closed and the gas is then similarly passed to the remaining ingot molds, if any, in the series and the-last exhaust valve similar-tothe'valve-Zl is then yclosed and the pressure in the system is then built up to the desired pressure, such as 2000 'pounds per Square inch, OI example, 0I' generally within the range of from about 1000 to.4000 pounds per square inch. The ingot molds on the tank cars may advantageously be furnished with separate or independent heating elements, such as tungsten rods or coils which may be electrically heated in the usual manner, or the noble gas passing to the first ingot mold I6 may be heated to the desired temperature, generally within the range from about 1330 F. to 2550 F. below the liquidus at which temperature range the ingot remains solid, but contains austenite, and the pressure of the gas is regulated to provide the desired pressure in the system. If the ingot molds which are added at the incoming end of the series are in a cold condition, the temperature of the ingots in the series is gradually increased by heat absorbed from the gas passing through the molds in accordance with the counter current principle, the gas at the incoming end, passing to the first mold, being at a temperature such as to heat the ingot therein to a temperature at which austenite is present, that is, without melting the metal. The rst ingot mold is permitted to cool in an atmosphere of the noble gas by closing the valves I8 and 2|, and then removing the mold with the ingot therein from the series, after which another ingot mold with an ingot therein may be added at the end of the line so as to pass through the system up to the point at which it contacts with fresh helium, or noble gas, so as to befirst in the series, whereby in passing through the system the temperature of the ingot is gradually increased and the ingot, while at a temperature at which austenite is present, remains quiescent for a time sufficient to permit occluded and dissolved foreign gases to be evolved or effused from the metal and taken up by the noble gas. As the noble gas passes through the series, it takes up more and more of the dissolved and adsorbed foreign gases, as oxygen, nitrogen and hydrogen, and during the passage forwardly through -the series, its temperature is gradually reduced and the pressure may be allowed to be correspondingly reduced, if desired, so that at the end of the series, the noble gas is in a condition in which it may be readily purified by passing through the chemical purifying system as indicated in Fig. 1 of the drawings. The purified gas may then be passed to a storage tank, as 48, and then may be reused in the same or a similar system.

It will be understood that in a large plant, it will be preferable to treat the ingots immediately after the metal is poured from a ladle into the molds, and the ingot molds may be treated on ingot cars in the manner indicated in Fig. 2 of the drawings in a series in the manner above explained, except that it will be unnecessary to separately heat the noble gas, which may be employed to assist in the cooling of the ingots, and may be passed consecutively from the outgoing ingot to the incoming ingot in the line whereby the gas becomes hotter and hotter in passing through the series, taking up more and more impurities in accordance with the counter current principle, the fresh helium gas, or other noble gas, passing to the most purified ingot in a series, which is that ingot which has passed from the incoming end through the series to the outgoing end and is ready to be discharged. It will be understood that the gas may be purified by separate chemical apparatus after having passed through the series or it may be used for an extended period of time over and over again through several series of treatments until the impurities or foreign gases have accumulated in the noble gas to such an extent as to require purication. Obviously, while the impure gas is being purified, a separate tank of purified noble gas may be used so as not to interfere with the continuous operation of the plant.

In Fig. 3 of the drawings is shown a bottom-fed type of ingot mold designated generally by the letter A and which type of mold lends itself very effectively to the carrying out of the process of the present invention. The procedure in connection with the bottom-fed mold shown in Fig. 5 of the drawings is that the metal is rst poured in the gate 24 at the top and rear of the mold. The sides 25 of the riser 26 are made of refactory material to hold in the heat. 'Ihe refractory material is encased by a cast iron portion 21 integral with the ingot mold A which rests on the usual pouring plate 28. The metal runs into the ingot mold through the opening 29 until the molten metal is at the proper height in the ingot mold. The top B is connected to the bottom by threading, or it may be made integral therewith by welding. The top contains the inlet valve 30 and exhaust valve 3i, and may also be provided with the lifting eye 33. The heated helium, or noble gas, which is under a high pressure, compresses or exerts pressure on the ingot from all sides and assists in removing the dissolved and adsorbed gases and causing collapsing of blow-holes in the metal, thus greatly improving the physical properties of the metal. After the ingot has solidied, the gas is pumped off or drawn off and the mold may then be lifted off the ingot by means of a suitable lifting device which may be attached through the opening at the top of the mold, after which the gate on the ingot may be burned off. This type of ingot mold prevents slag from getting into the molds, and prevents metal from spattering up the sides of the mold and forming cold shuts. This form of apparatus is particularly useful for carrying out the improved method of the invention for the reason that the hot gas prevents the top of the ingot from cooling before the bottom portion is cooled, or solidified.

It will be understood that various changes or modifications may be made in the method above described without departing from the spirit or the scope of the invention as defined in the annexed claims.

I claim:

1. In the manufacture of steel, a method for improving the physical properties thereof which comprises subjecting solid steel at a temperature between about 1330 F. and 2550 F., at which austenite is present, to an atmosphere of a noble gas surrounding said steel, said gas being under pressure between about 1,000 and 4,000 pounds per square inch, said steel being surrounded by said atmosphere under said pressure for a substantial period of quiescence during which occluded and dissolved gases in the steel become dispersed into the said noble gas atmosphere, thereafter cooling said steel to ordinary temperatures in said noble gas atmosphere while under said pressure and finally separating said steel from said noble gas atmosphere.

2. In the manufacture of steel, a method for improving the physical properties thereof which comprises subjecting solid steel at a temperature between about 1330 F. and 2550 F., at which austenite is present, to an atmosphere of a noble gas surrounding said steel, said gas being under pressure between about 1,000 and 4,000 pounds .per square inch, said steel being surrounded by said atmosphere under said pressure for a substantial period of quiescence during which occluded and dissolved gases in the steel become dispersed into the said noble gas atmosphere, chemically purifying said noble gas to remove impurities therefrom and recycling said noble gas into the process, thereafter cooling said steel to ordinary temperatures in said noble gas atmosphere while under said pressure and nally separating said steel from said noble gas atmosphere.

3. In the manufacture of steel, a method for improving the physical properties thereof which comprises subjecting solid steel at a temperature between about 1330 F. and 2550 F., at which austenite is present, to an atmosphere of substantially pure helium surrounding said steel, said helium being under pressure between about 1,000 and 4,000 pounds per square inch, said steel being surrounded by said helium at said temperature and under said pressure for a substantial period of quiescence during which occluded and dissolved gases in the steel become dispersed into said helium atmosphere, thereafter cooling said steel to ordinary temperatures in said helium atmosphere while under said pressure and finally separating said steel from said helium atmos- Y phere.

4. In the manufacture of steel, a continuous method for improving the physical properties thereof which comprises subjecting solid steel ingots in a series at a temperature between about 1330 F. and 2550 F., at which austenite is present, to an atmosphere of substantially pure hellum under pressure between about 1,000 and 4,000 pounds per square inch, said helium being passed into contact with the ingot first in the series and thereafter successively to each of the remaining ingots in the series, thereafter cooling the ingots successively to substantially room temperature in said helium atmosphere while under said pressure, purifying the used helium to remove carbon dioxide, water vapor, hydrogen, oxygen and nitrogen therefrom, recycling the purified helium into contact with ingots under treatment in the series and removing said cooled ingots successively from said series.

GEORGE R. BURKHARDT.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 314,004 Edwards Mar. 17, 1885 1,842,200 Ramage Jan. 19, 1932 2,057,518 Fraser et al. Oct. 13, 1936 FOREIGN PATENTS Number Country Date 338,409 Great Britain Nov. 20, 1930 

